Medaka Kurokami is the perfect honour student. She has exemplary grades, talent at any sport she tries her hand at, comes from a rich family, is exceptionally popular, and has just become the first ever freshman student to be elected School President! During her inauguration speech she proclaims that she will endeavour to help every student with any problem if they simply submit it to the newly instated suggestion box. But with a bare-bones student council consisting of only herself and her unwilling accomplice Zenkichi, people are unsure whether to take her seriously or not. Regardless, Medaka takes each suggestion and gives her all to fulfil any request, be it ridding the kendo hall of delinquents, writing a love letter, or helping a struggling art student find his muse.
The female leads in both series are quite similar. Both are insanely strong, very confident and somewhat open minded. The fact that one is rather smart while the other is not doesn't affect the similarity as much as one would expect. There many other similarities between those two and even the plot contains some similar themes. Anyway, if you liked the female lead in one series, you'll probably going to like the female lead in the other one (and maybe even the series itself).
If you liked the male lead in one of those series, you're probably going to like the one in the other series too. They break a number of shounen stereotypes, by actually being confident, cool etc. The biggest difference between them is that one of them is a pervert. I know it all sounds vague, but if you liked one of those guys, you ought to read the other series.
The male leads in those two series are somewhat similar. Can't really explain it, maybe it has something to do with the ability to push girls around (while in most shounen series it's the other way around). If you liked one of those two guys you'd probably want to give the other series a try (just keep in mind that Maji de Watashi ni Koi Shinasai! has more coherent story).